Field of the Invention
The present invention relates to a system for monitoring the degradation of a battery and a technique of computing the rate of degradation when the battery is left to stand.
Description of the Related Art
Recently-developed hybrid vehicles and plug-in hybrid vehicles are equipped with large-capacity batteries (secondary battery cells) as traveling and driving power sources. Since a battery degrades and the capacity thereof decreases due to use, there is a need to understand the degradation rate of the battery.
The degradation rate of the battery is computed on the basis of, for example, the amount of discharge of the battery and the integrated value of battery temperature (see Japanese Patent Laid-Open No. 2013-181875).
The battery degrades, however, depending on elapsed time and temperature not only when in use but also when not subjected to current input/output like when a vehicle is left unattended. Accordingly, the degradation rate may vary greatly according to temperature change if, for example, the vehicle is not used and left unattended for a prolonged period of time.
The system described in the abovementioned patent publication detects and integrates the amount of discharge of a battery and battery temperature at predetermined time intervals, in order to calculate the degradation rate of the battery. Accordingly, the power supplies of current and temperature detection means and an arithmetic device have to be kept turned on. The system therefore consumes electrical power and is suited neither for long-term monitoring nor for monitoring when a vehicle is left unattended in particular.